Tilt coupling

ABSTRACT

A tilt couple device having a pair of mounting members with each member having a wedge-shape cam. At least one of the cams has teeth on it that engages a pinion on an operating shaft. Rotation of the operating shaft causes the pinion to rotate one cam member relative to the other in order to change the inclination of one mounting surface relative to the other.

This invention relates to drawing apparatus which includes a drawingboard or easel for use by artists, draughtsmen and architects forexample. Such boards or easels may be used to support a sheet of canvas,card or paper whilst the user makes a sketch or drawing or does apainting or plan or writes upon it. This invention also relates to atilt coupling device for use in the drawing apparatus, but having otheruses also.

Existing drawing boards are often provided with some form of stand,enabling the board to be placed on a table or stood on the floor orground for use. The latter form of support is often used by artists forsketching or painting outdoor scenes. However, some artists find the.conspicuousness of using such a drawing board unacceptable, particularlyif they are novices in the field. In addition, existing supports are notideal for use at night or in inclement weather.

U.S. Pat. No. 3,739,478 discloses a clipboard for attachment to thesteering wheel of a motor vehicle. A circular baseplate has adjustablespring clips for snapping over a steering wheel, and a circular board isrotatably mounted on the baseplate. U.S. Pat. No. 4,139,217 discloses adesk which is provided with spring clips to mount on a steering wheel.In both of these earlier proposals the board is inclined at the sameangle as the steering wheel so that with most if not all motor vehiclesthe board may be in the wrong position for many uses.

In accordance with this invention there is provided a drawing apparatuscomprising a drawing board having mounting means for mounting thedrawing board on the steering wheel of a motor vehicle, the mountingmeans being arranged so that the drawing board can be mounted in aplurality of different inclinations relative to the wheel.

The mounting means may comprise a pair of limbs which project from therear of the drawing board and which can be folded to a stowed positionagainst the rear of the drawing board. The mounting means may furthercomprise a support plate which projects from the rear of the drawingboard and which can be folded to a stowed position generally parallelwith the rear of the board or easel. The support plate is preferablycoupled to a swivel plate which is coupled to the rear of the drawingboard for rotation about an axis which is substantially normal to theplane of the drawing board.

The drawing apparatus preferably includes a viewfinder comprising aviewing member provided with a grid or index marks, the viewing memberbeing mounted on an arm arrangement which is in turn secured to a devicee.g. a clamp for attaching to the drawing board.

It is known in some precision optical instruments to vary theinclination of a main part of the instrument relative to a base byrelative rotation of a pair of superimposed wedge-shaped cam members.Rotation is achieved simply by a pair of handles each secured to arespective cam member. Moreover, the instrument is held to the base by aspring metal joint located internally of the cam members, with theresult that the instrument is only poorly fixed relative to the base.

In accordance with this invention there is provided a tilt couplingdevice comprising first and second mounting members having twowedge-shaped cam members, at least one of the cam members beingrotatable relative to the other cam member and to the adjacent mountingmember in order to change the inclination of one mounting memberrelative to the other, the device further comprising a series of teethformed on one of the cam members, and a pinion meshed with said seriesof teeth and carried on an operating shaft, such that rotation of theoperating shaft causes rotation of said one cam member relative to theother.

Preferably a slip ring is disposed between the opposed cam surfaces ofthe two cam members, the operating shaft being mounted to the slip ringand the pinion being mounted both with said series of teeth formed onsaid one cam member and with a series of teeth formed on the other cammember.

The tilt coupling device maybe used in the drawing apparatus, thedrawing board being mounted to the first mounting member of the tiltcoupling device and the second mounting member of the tilt couplingdevice being attachable to the steering wheel of a vehicle.

Embodiments of this invention will now be described by way of examplesonly and with reference to the accompanying drawings, in which:

FIG. 1 is a general perspective view of a first embodiment of drawingapparatus in accordance with the invention, including inset details ofparts of the apparatus;

FIG. 2 is a perspective rear view of the drawing board only, when foldeddown;

FIG. 3 is an enlarged view of a viewfinder included in the drawingapparatus;

FIGS. 4 to 9 show the drawing board mounted on a steering wheel in sixdifferent positions;

FIG. 10 is a perspective view of a second embodiment of drawingapparatus;

FIG. 11 is an axial section through a tilt coupling device forming partof the drawing apparatus of FIG. 10; and

FIG. 12 is a plan view, partly in section, of the lower cam member ofthe tilt coupling device.

Referring to FIG. 1 of the drawings, there is shown a drawing apparatuswhich comprises a substantially rectangular board 1 having a swivelplate 2 secured parallel to its rear face by a pivot 3 to rotate aboutan axis normal to the plane of the board and through substantially thecentre of the board. A flat, elongate support plate 4 is hinged at 5 toone edge of the swivel plate 2 such that it can be swung from anextended position (FIG. 1) disposed at an angle of about 95° to 100° tothe swivel plate, to a stowed position (FIG. 2) lying against the swivelplate. Towards the top of the board 1 a pair of spaced L-shaped hookelements 6 are hinged to the rear face of the board with the shorterlimbs of the L projecting radially towards the pivot 3. The hookelements 6 can be swung from the extended position shown in FIG. 1 to astowed position shown in FIG. 2, in which their longer limbs extendradially of the pivot 3 and their shorter limbs abut the rear of theboard.

A support bar 10 having inturned flanges 11 at each end can be engagedover the board 1 with the flanges 11 located behind the side edges ofthe board. The bar can thus be slid up and down the board to anyrequired position. The support bar may have a simple frictionalengagement with the board to retain it in the required position, and thebar may thus act as a support for the lower edge of a sheet of paper orlike material placed on the board. Instead of a friction grip the barcould be provided with clamping screws. In the illustrated board theinternal faces at each end of the bar are provided with gripping pads101, 102. One of the pads 101 is fixed and may have packing shims 103placed behind its rear face. The other pad 102 is connected to a plunger104 that is operable by a pivoted cam lever 105. A cam 106 on the camlever 105 operates the plunger 104 so that as the lever 105 is movedfrom a horizontal position towards a depending vertical position asshown, the pad 102 is moved towards the other pad 101 to clamp the edgesof the board 1 between the pads. The shims 103 provide fine adjustmentfor optimum clamping. A further adjustable bar can be provided so thatthe top and bottom edges of a canvas can be clamped between the twobars.

Spring clips 14 may also be provided to engage over an edge of theboard, and these too can be used to secure a sheet of paper or the liketo the board.

The apparatus also includes a viewfinder indicated generally at 16 whichcan be used to support a flat rectangular viewing frame 17. The viewingframe is one of a set, two of which, 17' and 17", are shown in moredetail in FIG. 3. These frames all fit snugly inside one another, andthe corresponding inner and outer edges of each frame are provided withequal numbers of regularly spaced peripheral index marks 171. Each frameis slightly smaller than standard paper size (A4, A5 etc.) to allow theframe to be superimposed centrally on a sheet of paper of theappropriate size. The frame is then used as a template to draw a borderon the paper, within which index marks are then added corresponding tothose on the outer edge of the frame.

Referring to FIG. 1, the frame to be used is removably secured, e.g. bya clip with a friction grip, to a ball joint 18. This ball joint ismounted at one end of a first arm 19 which is hinged at 20 to a secondarm 21. The hinge 20 incorporates a locking screw 22 for fixing theangular relationship between the arms 19 and 21. The second arm 21carries a clamp 23 including a pair of jaws which are spring loaded intoa closed position. The clamp is adjustably secured to the arm 21 by anapertured slide member 24 provided with a locking screw 24a, enablingthe clamp to be secured at any desired position along the second arm 21.

The clamp 23 can be releasably secured to any suitable fixture withinthe vehicle, such as the edge of the board 1 or part of the trim of thevehicle. A magnet or suction cup could be used in place of the clamp 23.The user can adjust the viewing frame 17 into his/her field of vision sothat a view or object outside the vehicle can be seen through thecentral aperture of the frame. The index marks on the inner edge of theframe correspond with those marked on the paper, albeit in a smallerscale, and can thus be used to guide the user in accurately transferringthe view to the paper in the form of a drawing or sketch.

The angle of the board can be adjusted to the most comfortable positionfor a particular use by mounting the board on a steering wheel in one ofa number of possible configurations. In the case of a steering wheelinclined at a relatively steep angle (FIGS. 4 to 6) the hook elements 6can be extended and hooked over the top edge of the steering wheel: thesupport plate 4 is in a stowed position and the board rests against thelower edge of the wheel but the shorter limbs of the hook elements 6abut the underside of the wheel. The board 1 will thus be inclined at arelatively steep angle as shown in FIG. 4. The board will however alsorest stably if it is moved to lie flat against the wheel and thereforeat a shallower angle, as shown in FIG. 5. By pivoting the support plate4 to its extended position to rest across the steering wheel as shown inFIG. 6, the board can be inclinded at an even shallower angle. In thisconfiguration the swivel plate can be rotated about the the pivot 3 totilt the board to right or left, thereby improving the performance ofthe board for right or left-handed users respectively.

In the case of a steering wheel which is inclined at a smaller angle asshown in FIGS. 7 to 9, the board can be inverted and the support plate 4extended to rest across the steering wheel with the hook elements 6,which are also extended, located inside the wheel rim (FIG. 7). In thisconfiguration the board is inclined at a relatively steep angle, and canbe tilted to right or left by rotating the support plate about the pivot3 for right or left handed use. By folding the support plate to thestowed position (FIG. 8) the board will adopt a shallower anglegenerally parallel to the plane of the wheel. Finally, by mounting theboard on the wheel in a non-inverted position with the support plate 4extended and the hook elements located outside the upper rim of thewheel (FIG. 9) the board can be mounted almost horizontal. In each casethe board is firmly mounted against the wheel in a stable condition.

The board is easy to mount on the steering wheel when the vehicle isparked and is equally quickly removed again before driving off.

An artist's easel of the kind comprising a spine and a pair oftransverse clamping members with adjustable spacing can be used in placeof the board 1.

The board could be provided with a parallel motion or pantograph systemof known form.

FIG. 10 shows a second embodiment of drawing apparatus in accordancewith this invention, comprising a drawing board 1 having a tilt couplingdevice 5 mounted to its underside, the device 5 being secured on amounting member 7 which is attachable to a vehicle steering wheel. Themember 7 has four radially projecting arms provided with hooks 9 forengaging around the rim of the steering wheel: the hooks are slidablerelative to the member 7 so that they can be slid inwards to engage thewheel once the assembly has been placed on the latter.

The tilt coupling device includes a pair of axially spaced circular topand bottom plates 25, 26 (shown only in FIG. 11) each having an annularlocating shoulder 27 on its inner face, which in the case of the topplate 25 is formed by two plate sections which are fastened together.The top and bottom plates 25 and 26 also contain central apertures 46and 47, which enables the device to be used in certain opticalapplications (instead of in the drawing apparatus) where it is necessaryfor light, or a beam of light, to pass axially through the device. Thetop and bottom plates are axially spaced by two cam members 28, 29 whichcan be axially aligned to define a hollow cylinder, as shown. Theopposite outer ends of the two cam members are located in the shoulders27 of the top and bottom plates so that each plate 25 or 26 may beturned relative to its respective cam member, whereas the adjacent endsof the cam members are formed on parallel planes A--A', B--B' which areinclined to the axis of the cylinder. The opposed, arcuate faces of thecam members are provided with external annular female shoulders 48 and49 which receive and locate an intervening slip ring 50. A radiallyextending operating shaft 51 is rotatably mounted in the slip ring, andthe inner end of the shaft carries a toothed pinion 52 which engages twosets of radially extending, circumferentially spaced teeth 53, 54 formedon the opposed faces of the cam members 28 and 29.

The plates 25 and 26 are held together by a universal joint indicatedgenerally at 32. This joint comprises two pairs of diametrically opposedlimbs 33 and 34, one pair being secured to each of the plates 25 and 26.A ring 41 is located between the limbs 33 and 34 and is pivotaly coupledthereto by two pairs of pivot pins 42-45 to pivot about two mutuallyperpendicular axes. The universal joint thus permits angulardisplacement of the plates 25 and 26 whilst at the same time preventingrelative rotation between the plates about their axes.

In use, the plates 25 and 26 are secured to two components which arerequired to be angularly adjustable relatively to each other: in thecase of the drawing apparatus shown in FIG. 10, the top plate is fixedto or forms part of the drawing board 1 and the bottom plate is fixed toor forms part of the mounting member 7. The cams are relatively rotatedto alter the inclination of the mounting plates by rotating theoperating shaft 51 about its own axis. Thus, the top and bottom plates25, 26, and hence the components to which they are connected, willgradually move from a parallel position to a mutually inclined position.The maximum relative inclination is twice the angle between plane A--A'or B--B' and the axis of the respective cam member. The direction ofinclination of the plates 25 and 26 can also be adjusted through 360°whilst the angle of inclination remains the same, by rotating the shaftcircumferentially of the plates so that the cam members rotate togetherwith each other and relative to the top and bottom plates.

In some applications it may be sufficient for the two series of teeth53, 54 to extend for less than 360° around the cams, say through 110°.The opposed faces of the cam members 28 and 29 and the respective plates25 and 26 could be provided with thrust bearing in applications wherethe coupling could be used to transmit a drive torque. In this case theuniversal joint 32 could be replaced by a constant velocity joint toensure a smoother transmission of rotational movement when the couplingis set at an angle.

I claim:
 1. A tilt coupling device comprising first and second mountingmembers having two wedge-shaped cam members, at least one of the cammembers being rotatable relative to the other cam member and to theadjacent mounting member in order to change the inclination of onemounting member relative to the other, the device further comprising aseries of teeth formed on one of the cam members, and a pinion meshedwith said series of teeth and carried on an operating shaft such thatrotation of the operating shaft causes rotation of said one cam memberrelative to the other.
 2. A tilt coupling device as claimed in claim 1,comprising a slip ring disposed between the opposed cam surfaces of thetwo cam members, the operating shaft being mounted to the slip ring andthe pinion being meshed both with said series of teeth formed on saidone cam member and with a series of teeth formed on the other cammember.